Tracing cloth and the like and method of preparing same



Patented Jan. 9, 1951 2,55'Lili TBACING CLOTH AND THE LIKE AN!) METHOD-OF PREPARING SAME Horace Wood, Jan, Wal efield-, Mass., assignor toMonsanto. ilhemi'cal' Company, St. Louis, Mo., a

corporation of Delaware No Drawing. Application July, 1, 1948, SerialNo. 36,443.

14; Claims. 1

The present invention relates to a method of preparing improved tracingcloth, hol'land cloth and thelike and to the-coated articles-per se. Itmore particularly relates to a method of preparing; improved tracingcloth and the likewhich is especially adapted to besensitized with aphotographic emulsion coating.

Tracing cloth has, in general, been manufacured heretofore by; firstimpregnating a woven cotton fabric, fabricated; from. fine lon staple oon y ms; with starcnewatermixture, after which, the, f abric; is; dried;and-guper-calendered or friction-calendered ata; high temperature as,for example, about no? F It is. not: possible todirectly; coat, the:starch impregnated fabric; with a photographic gelatin emulsion; sincethestarch is Water sensitive and, isremoved from; the: fabric to a,considerable extent onimmersion in water and, therefore, could: not,suitablywithstand the d v lop ng, and Washing. p ess s: normallyemployed in photographic, reproduction work. Therefore. order to,employ, starch impreghated. abrics or is useithas be n e ss y tocoatsuch fabricswith a clear water-resistant film, r ating. fnirncellulosa ethylicellulose or he ik antecedent o the application theref a phot r phi u si nc atina.

The; foregoing method leaves much to be, desired. For examplait isdiilicult to amalyw a completely'protective nitrocellulose or other.water resistant coating over the starch impregnant. Such-acoating isnecessary, however, in. order to prevent water from swelling the starchand;c au sin image distortion and/or peeling of the protective coatinand the like. In practice com plete protection of the starch from thewater used in the photographic reproduction processes is not alwaysachieved with; the result that the photographic reproduction must attimes be rejected as not being suitable for its intendeduse whether itbe. used as a master print or" a copy. 'Ifheabove described method isalso relatively in,- efii'oient invthatyextraisteps are employedinmanufacturing the lacquered. tracing cloth, and, therefore. requires :1the use of I considerable extra cqu nmen randclabor.

Ifhe same difiicultiesexist; in varying degrees the; manufacture, of;holland: cloth, surveying es; meas r nge-tapesand: the like.

The present; invention; provides: a. process. for m nu a urin tra ingclothL holland cloth. and the like, which is; not; only: efficiently.and; economically carried out, but: which-also eliminates many. oftheforflgilihfl; ind'bther difficulties and Qi e ra e s he!prnrartzprocessesiandrtne rretluc ssmt pa ed bnsuch processes/e.

It is one object of the present invention to manufacture a tracingcloth, holland cloth and the like for photographic and non-photographicuses by employin a coating impregnant which is notonly water-resistantand flexible, but which is also capable of being suitablysuper-calendered and glazed.

A further object of the invention is to provide a simple and efiicientprocess for manufacturing tracing'cloth especially suitable forphotographic reproduction uses.

A further object of the invention is to produce by the use of a singleimpregnant a tracing cloth which is especially adapted to be sensitizedwith photographic emulsion coatings and which can be rocessed in Watersolutions Without the use of an additional water-resistant coating.

Still further objects and advantages of the present invention willappear from the following description and the appended claims.

The invention is practiced, in general, by first impregnating a fabric,which is suitable as a base for tracing cloth, holland cloth, measuringtape or the like, with an organic solvent solution com-- prising as anessential film-forming material a copolymer of a polymerizable vinylcompound havin the structural formula RCH=CH2, where R is a phenyl orsubstituted pheny-l radical, with a secondary alkyl half ester of anethylene -a,e-dicarboxylic acid, in which the alkyl group contains from:4 to 12' carbon atoms. The impregnating solution preferably alsocontains a minor proportion, based on said copolymer, of polyviny1butyral. After the fabric is impregnated in the manner indicated, it isheated to evaporate the organic solvent or dried in suitable manner. andis then frictionecalendered or supercalendered using heat and pressureto glaze the film-forming materialor materials.

A clear coating is formed by. the above procedure, but such coating maybe opacified, if desred, by incorporating a small amount of pigment,flatting agent and the like in the impregnation solution. Thesuper-calendered fabric possesses, sufficient water-resistance to beemployed as a non-sensitized tracing, cloth, as holland cloth and thelike. When the superecal- .endereo. fabric is to be employed in themanu- Ifacture of lightsensit've tracing cloth and the like, theresistance of the coating thereon to water and organic solvents ispreferably improved, however, by incorporating in theimpregnatingsolution a relatively small proportion, say

about 0.5 to 5% by weight, of a compound'which is capable ofcross-linking the carboxyl' groups in the copolymer. As 'examples ofsuch crosslinking compounds may be mentioned formaldehyde;amino-aldehyde monomeric or low polymeric resins; phenol-formaldehydemonomeric or low polymeric resins; alkylene polyamines such as ethylenediamine, propylene diamine, butylene diamine and the Ike; andpolyglycols such as triethylene glycol, tetraethylene glycol and thelike. When the impregnating solution contains such compounds, thefilm-forming materials described above are at least partiallycrosslinked or otherwise inter-reacted to produce a film or coatingwhich is substantially resistant to the organic solvents in which theyare originally soluble. The cross-linking or mutual reaction of at leasta portion of the film-forming materials in the presence of such across-linking compound is accelerated by heat and/or an acid typecatalyst. It is preferable when the above compounds are employed to heatthe supercalendered fabrics at temperatures between about 225 F. to 330F. in the presence of an acid catalyst such as tartaric acid, ethylphosphoric acid, oxalic acid, citric acid or the like as, for example,for a period of from 1 to minutes, depending upon the temperature used,to accelerate the cross-linking or curing of the film-forming materials.Normally, the above copolymers and the polyvinyl butyral resin mutuallyreact or cross-link at least partially merely on aging without the useof such cross-linking compounds, but the cross-linking generallyproceeds at a relatively slow rate under such conditions.

Of the above described cross-linking compounds or agents, theamino-aldehyde resins are preferably employed. As examples of suchresins may be mentioned urea-formaldehyde resins such as methylol ureaand di-methylol urea; alkylated urea-formaldehyde resins or alkoxy alkylurea resins such as methoxy methy1 urea, di- (methoxy methyl) urea,(methoxy methyl) methylol urea and the like; melamine-aldehyde resinssuch as the methylol melamines and particularly those having from 1 to 4methylol groups per mol of melamine and the like; and alkylatedmelamine-aldehyde resins or alkoxy alkyl melamine resins such as(methoxy methyl) monomethylol melamine, di-(methoxy methyl) monomethylolmelamine, di-(methoxy methyl) dimethylol melamine and the like ormixtures thereof. Of these the methyl ethers of methylol melamines ormethylated melamine-formaldehyde resins of the type last described arepreferred.

The copolymers employed herein as essential film-forming materials maybe prepared in a variety of ways, but are generally prepared bycopolymerizing by various Well-known methods a polymerizable vinylcompound, having the structural formula R,CH=CH2, Where R is a phenylradical, a halogen substituted phenyl radical such as chloro phenyl,dichlor phenyl and the like, or a methyl substituted phenyl radical suchas methyl phenyl, dimethyl phenyl and the like with a secondary halfester of an ethylene afi-dlcarboxylic acid in which the alkyl groupcontains from 4 to 12 carbon atoms and preferably 6 to 10 carbon atoms.The vinyl compound and half ester are generally copolymerized in a molalratio Varying between about 2:1 to 1:1 and preferably in a molal ratioof 1.5:1 to 1.121. The secondary alkyl ester of an ethyleneafi-dicarboxylic acid may also comprise a small proportion of anethylene a,/3-dicarboxylic acid or anhydride.

As examples of such secondary half esters may Cir bemention-edsec.-butylacid maleate,butylmethyl carbinyl acid maleate, methyl amylcarbinyl acid maleate, methyl hexyl carbinyl acid maleate, methyl heptylcarb'nyl acid maleate, methyl decyl carbinyl acid maleate and the like,the corresponding acid fumarates and the like.

The secondary alkyl half esters are prepared, in general, by reacting asecondary alcohol as, for example, secondary butyl alcohol, methylisobutyl carbinol and the like with an ethylene a,/i-dicarboxylic acidor anhydride such as maleic acid, fumaric acid, maleic anhydride and thelike. The alcohol and acid or anhydride are preferably reacted in amolal ratio varying between about lzl to 1:1.6. The unreacted alcohol,acid or anhydride can be removed or separated from the secondary alkylester so formed, if desired, or the entire mass can be employed in thesubsequent polymerization with the above described vinyl compounds.

The above described copolymers may be prepared, if the secondary alkylhalf ester and vinyl compound are mutually soluble, by masspolymerization which involves heating the reactants or monomers attemperatures varying between about to 300 0., usually, in the presenceof a catalyst as, for example, a peroxide catalyst such as benzoylperoxide. If the half-ester and vinyl compound are not mutually soluble,the copolymer may be prepared, for example, by emulsion polymerizing themonomers or by copolymerizing the monomers in a solvent for the monomersand copolymer. In the latter case the copolymer may be precipitatedafter it is formed, for example, by adding an inert diluent to thereaction mixture. The precipitated copolymer can then be separated fromthe mixture by filtration, centrifuging and the like.

The copolymers employed in the present invention are, in general,soluble in a wide variety of organic solvents and solvent mixtures. Asexamples of these may be mentioned: alcohols such as methanol, ethanol,isopropanol, n-propanol, butanol and the like; esters of acetic acidsuch as ethyl acetate, propyl acetate, butyl acetate and. the like;ketones such as acetone, diethyl ketone, methyl ethyl ketone, methylisobutyl ketone and the like; mixtures of alcohols or acetates witharomatic or aliphatic hydrocarbons as, for example, such mixtures asethanol-toluol, propanol-toluol, ethyl acetate-toluol, ethanolpetroleumnaphtha fractions; propanol-petroleum naphtha fractions, ethylacetate-petroleum naphtha fractions and the like. The foregoingsolvents, generally Speaking, are also solvents for a mixture of theabove copolymers, polyvinyl butyral and the above describedcross-linking compounds.

Solutions of the above copolymers in the foregoing solvents or solventmixtures can be applied to a fabric suitable for tracing cloth, hollandcloth and the like in various ways as, for example, by knife coating,roll coating, and the like or by immersing the fabric in the solutionand then removing the excess solution. Other methods of application mayalso be employed. The quantity of polymer present in such solution maybe varied considerably depending upon the means used to apply thesolution to the fabric, the particular end use of the fabric, theviscosity of the copolymer in the solution, the quantity of otherfilm-forming material or compounds of the type hereinbefore describedpresent in the solution etc. In general, from about 5 to 30% by weight.bf' the" copolyme'r is '-used in the impregnating s'oluti'on when su'chcopolymer is present as the sole film forming material. 'When,in-addition, polyvinyl butyraland/or the 'above' described cross-linking-compounds' are also employed in In a preferred embodiment "of theinvention polyvinyl butyral and a cross-linking compound or agent of thetype hereinbefore described are employed along with theabove describedcopolymers to give improved flexibility and-solvent resistance to' thetracing cloth. The quantity of polyvinyl butyral present in theimpregnating "solution'depends to'a' considerable extent on the "degreeof flexibility desired in the finished cloth or fabric. weight ofpolyvinyl "butyral, based on the 'copoly- 'mer', is imployed intheimpregnating solution,

In general, from about 1 to 35% by while from about to by weight ofpolyvinyl buty'ral; based on the copolymer, is preferably employed.

Afurther understanding of the present in- 'vention will be obtained fromthe following examples which are intended to be illustrative of theinvention, but not limitative "of the scope ."thereof, parts andpercentages being by weight.

thus prepared was copolymerized with about 115 molecular proportions'ofstyrene in the presence 1 *of about 0.003 molecular proportion ofbenzoyl I peroxide.

The reaction'was initiated at about C.and this temperature wasmaintainedduring the periodof rapid heat evolution. The temperature ofthe mass was then raised to 120 C. fora period of 1 /2 hours to completethe reaction. On cooling, ahard, "glassy resin was obtained which wascom'minuted to "make it more readily soluble.

An impregnating solution was made up conta ning 20 parts of copolymer A(as prepared above) and parts of specialdenatured alcohol No. l and thissolution wasknife coated onto a bleached cotton woven fabric weighing1.9 oz.

per square yard and having about warp ends.- and '87 filling yarnsper-inch. The impregnated fabric was 'driedat about for approximately 5minutes "in a tunnel drier. The other surface of the fabric was thenimpregnated and dried in a similar manner and the fabric was thenfriction-calenderedusing a three roll friction-calender. The frictionroll of the calender was rotated at a peripheral velocity 2 timesgreater than the peripheral velocity of the fabric rolls. During thefriction-calcnderingoperation,

Example II SOIfitiehwas-prepared "Whi h "cont med 14 p rtsb 'c e'polymr-A (prepareaas dsb bed ih jE-kahlble -I), --6'- par tS(if-polyvinyl "sa ty anc ents of'speci'al denatured alcohol ti'on wasronocated onto a ti; n-ratrrc weighing--r.c; ez;-persquare nd ha'ving 85war ends "ahd B'T filling yarns inch. The inipregnated abscess driedatates l-00" F.- o'r (l fniiiutes. The-othersurface 'of the at was mpre'g'nated -and dried by a i131 pi-oced iire and the fabric was thengiven passes thfo'li gha three IG'I-I fl'lCti-OI'IECaIB'Iider.

The friction roll of the calender 'was driven" at "tihresthe:"peripheral velocity of the feed rolls. ehiper'atlire of"th'e -rolls'wasaboi1t*320 F. *and the preset-teen "the fabric was about 15 tons *peliiiear Thesurfac'ebf the fabric which een' exposed to the friction rollwas smooth my grazed. 1 116;tracing cloth eo pioduce'd "I y waterresrstant and possessed good flexibility.

-A-n impregnating solution was prepared which contained l7.5 .parts ofcopolymer A (prepared as described in Example I), 7.5 parts of polyvinyl'butyral; 2.1- parts of anaqueous solution consisting-of-60%'byweightofdi-(methoXymethyl) dirnethylol melamine and 72.9 parts of asolvent mixture consisting of"40 special denatured alcohol No.-l and 66%toluol. This solution was 'kn'ife coatedonto a. woven bleached cottonfabric having substantially the same weighta-nd construction as thatdescribed in Example- I. The fabric was dried at about-15F. forErminutes and the other surface was then impregnated with the solutionand dried using the same procedure.

Thedry impregnated fabric was given three passes through a three rollfriction-calender wherein the friction roll "was driven at 3 timestheperipher-al velocity of the feeding rolls. .The

temperature of the rolls was maintained at about 315 F. and the pressureon the fabric was approximately 13.5 tons per linear inch. The tracingcloth was then heated to a temperature of 250 to 260? F. for a period of5 minutes to cure or cross-link the film-forming materials.

The cured tracing cloth ishighly flexible and co resistant to water,alcohol, and alcohol-hydrocarbon mixtures. 'It is also resistant toother :erganic liquids which are normally solvents for the copolymerandpolyvinyl butyral.

Thepolyvinyl butyral employed in the foregoing examples was prepared bycondensing 'buty-raldehyde with a'partially hydrolyzed polyvinyl acetateand contained on aweight basis 1'7 to20'% hydroxygroups calculatedas'polyvinyl alcohol; less than 3 acetate groups calculated as 7 0polyvinyl acetate and the remainder substantially butyraldehyde acetal.Instead of this specific polyvinyl butyral other polyvinylbutyralshaving lower hydroxy contents, higher acetate contents and/or lowerviscosity may be employed. In fl l-r he,l perties of the film formedrrcm the foregoing copolymers together with polyvinyl -butyra1 as, forexample, extensibility, flexibility and hardness will depend to acertain extent on the particular composition of the polyvinyl butyraland the method employed in preparing it. For these reasons, it will beapparent that the im- -.pregnating solutions described herein may bemodified to a certain extent depending upon the characteristics of thepolyvinyl butyral that is.

employed.

In the foregoing description and examples other conditions of drying andsuper-calendering the impregnated fabric may be used. For example, theimpregnated cloth may be dried at any temperature which drives off thesolvent contained in the impregnating solution, but is preferably driedat temperatures which allow the solvent to be released at such a ratewhereby formation of blisters or bubbles on the fabric surface isavoided. If speed of drying is unimportant the impregnated fabric can bedried at normal room temperatures. The fabric can be driedsatisfactorily, for example, at temperatures varying between about 90 to120 F.

Calendering may be carried out by using other means and conditions thanthose described above. For example, the dried impregnated fabric may besuper-calendered by hand ironing using a hot iron to cause thermoplasticflow of the coplymer and polyvinyl butyral, if the latter is alsoemployed. When super-calendering is effected by friction-calendering thevarious conditions of operating the friction calender may be varieddepending upon the type of apparatus employed and the end use of theimpregnated and calendered fabric. In general, the impregnated fabric issuper-calendered at temperatures and pressures which will cause thecopolymer to soften or flow into a substantially continuous film orsurface. Suitable temperatures for super-calendering vary between about275 to 330 F., while temperatures of about 310 to 325 F. are preferablyemployed. However, other temperatures may be used depending upon theparticular copolymer used and the ratio of copolymer to polyvinylbutyral employed in the impregnating solution.

What is claimed is:

'1. A method of producing tracing cloth which comprises impregnating aWoven cotton fabric which is suitable as a base for tracing cloth withanorganic solvent solution comprising 1) from to 30% by weight of acopolymer consisting of a secondary alkyl half ester of an ethylene 1,5dicarboxylic acid selected from the group consisting of maleic andfumaric acids, and a polymerizable vinyl compound having the structuralformula: RCH=CH2, where R is selected from the group consisting of aphenyl, halogen substituted phenyl and methyl substituted phenylradical, said half ester and said vinyl compound being copolymerized ina molal ratio between 1:1 and 1:2, (2) a minor proportion, based on saidcopolymer, of polyvinyl butyral, (3) from 0.5 to 5% by weight of acompound selected from the group consisting of formaldehyde,phenol-formaldehyde rcsins,urea-aldehyde resins, alkoxy alkyl urearesins, melamine-aldehyde resins, alkoxy alkyl melamine resins, alkylenepolyamines and polyglyco-ls and (4) an organic solvent for the foregoingingredients, said solution comprising from 6 to 32% by weight of solids;drying said fabric and then friction-calendering said fabric. 2. Amethod of producing tracing cloth which comprises impregnating a wovencotton fabric which is suitable as a base for tracing cloth with anorganic solvent solution comprising (1) from 5 to 30% by weight of acopolymer consisting of a secondary alkyl-half ester of an ethylene (1,3dicarboxylic acid selected from the group consisting of maleic andfumaric acids, in which the alkyl group contains from 4 to 12 carbonatoms, and styrene, said half ester and styrene being copolymerized in amolal ratio between 1:1 and 1:2, (2) a minor proportion, based on saidcopolymer, of polyvinyl butyral, (3) from 0.5 to 5% by weight of acompound selected from the group consisting of formaldehyde,phenol-formaldehyde resins,,urea-aldehyde resins, alkoxy alkyl urearesins, melamine-aldehyde resins, alkoxy alkyl melamine resins, alkylenepolyamines and polyglycols and (4) an organic solvent for the foregoingingredients, said solution comprising from 6 to 32% by weight of solids;drying said fabric and then friction-calenderin-g said fabric. 3. Amethod of producing tracing cloth which comprises impregnating a wovencotton fabric which is suitable as a base for tracing cloth with anorganic solvent solution comprising (1) from 5 to 30% by weight of acopolymer consisting of a secondary alkyl half ester of an ethylene ,3dicarboxylic acid selected from the group consisting of maleic andfumaric acids, in which the alkyl group contains from 6 to 10 carbonatoms, and styrene, said half ester and styrene being copolymerized in amolal ratio between 1:1 and 1:2, (2) a minor proportion, based on saidcopolymer, of polyvinyl butyral, (3) from 0.5 to 5% by weight of amethyl ether of methylol melamine and (4) an organic solvent for theforegoin ingredients, said solution comprising from 6 to 32% by weightof solids; drying said fabric and then friction-calendering said fabric.4. A method according to claim 3, but further characterized in that thesecondary alkyl half ester is methyl isobutyl carbinyl acid maleate.

5. A method according to claim 3, but further characterized in that thesecondary alkyl half ester is methyl amyl carbinyl acid maleate.

6. A method according to claim 3, but further characterized in that thesecondary alkyl half ester is methyl hexyl carbinyl acid maleate.

7. A friction-calendered tracing cloth which consists essentially of awoven cotton fabric suitable as a base for tracing cloth impregnatedwith a copolymer consisting of a secondary alkyl half ester of anethylene (1, 8 dicarboxylic acid selected from the group consisting ofmaleic and fumaric acids, and a polymerizable vinyl compound having thestructural formula: RCH=CH2, where R is a member of the class consistingof a phenyl, halogen substituted phenyl and methyl substituted phenylradical, said half ester and said vinyl compound being cogolymerized ina molal ratio between 1:1 and l:

8. A friction-calendered tracing cloth which consists essentially of awoven cotton fabric suitable as a base for tracing cloth impregnatedwith 1) a copolymer consisting of a secondary alkyl half ester of anethylene afi dicarboxylic acid selected from the group consisting ofmaleic and fumaric acids, and a polymerizable vinyl compound having thestructural formula: R-CH=CH2, where R is selected from the groupconsisting of a phenyl, halogen substituted phenyl and methylsubstituted phenyl radical, said half ester and said vinyl compoundbeing copolymerized in a molal ratio between 1:1 and 1:2, and (2) aminor proportion, based on said copolymer, of polyvinyl butyral.

9. A friction-calendered tracing cloth which consists essentially of awoven cotton fabric suitable as a base for tracing cloth impregnatedwith (l) a copolymer consisting of a secondary alkyl half ester of anethylene afi dicarboxylic acid selected from the group consisting ofmaleic and fumaric acids, and a polymerizable vinyl compound having thestructural formula:

Where R is selected from the group consisting of a phenyl, halogensubstituted phenyl and methyl substituted phenyl radical, said halfester and said vinyl compound being copolymerized in a molal ratiobetween 1:1 and 1:2, (2) a minor proportion, based on said copolymer, ofpolyvinyl butyral and (3) a small proportion of a compound selected fromthe groupconsisting of formaldehyde, phenol formaldehyde resins,urea-aldehyde resins, alkoxy alkyl urea resins, melamine-aldehyderesins, alkoxy alkyl melamine resins, alkylene polyamines andpolyglycols, said copolymer, butyral and last named compound being atleast partly inter-reacted.

10. A friction-calendered tracing cloth which consists essentially of awoven cotton fabric suitable as a base for tracing cloth impregnatedwith (l) a copolymer consisting of a secondary alkyl half ester of anethylene ,5 dicarboxylic acid selected from the group consisting ofmaleic and fumaric acids, in which the alkyl group contains from 4 to 12carbon atoms, and styrene, said half ester and styrene beingcopolymerized in a molal ratio between 1:1 and 1:2, (2) a minorproportion, based on said copolymer, of polyvinyl butyral and (3) asmall proportion of a compound selected from the group consisting offormaldehyde, phenol-formaldehyde resins, ureaaldehyde resins, alkoxyalkyl urea resins, melamine-aldehyde resins, alkoxy alkyl melamineresins, alkylene polyamines and polyglycols, said copolymer, butyral andlast named compound being at least partly inter-reacted.

11. A friction-calendered tracing cloth which consists essentially of awoven cotton fabric suitable as a base for tracing cloth impregnatedwith (1) a copolymer consisting of a secondary alkyl half ester f anethylene 11,5 dicarboxylic acid selected from the group consisting ofmaleic and fumaric acids, in which the alkyl group contains from 6 to 10carbon atoms, and styrene, said half ester and styrene beingcopolymerized in a molal ratio between 1:1 and 1:2, (2) a minorproportion, based on said copolymer, of polyvinyl butyral and (3) asmall proportion of a methyl ether of methylol melamine, said copolymer,

10 butyral and methyl ether being at least partly inter-reacted.

12. A friction-calendered tracing cloth which consists essentially of awoven cotton fabric suitable as a base for tracing cloth impregnatedwith (1) a copolymer consisting of methyl isobutyl carbinyl acid maleateand styrene, said maleate and styrene being copolymerized in a binylacid maleate and styrene, said maleate and styrene being copolymerizedin a molal ratio between 1:1 and 1:2, (2) a minor proportion, based onsaid copolymer, of polyvinyl butyral and (3) a small proportion of amethyl ether of methylol melamine, said copolymer, butyral and methylether being at least partly inter-reacted. 14. A friction-calenderedtracing cloth which consists essentially of a woven cotton fabricsuitable as a base for tracing cloth impregnated with (1) a copolymerconsisting of methyl hexyl carbinyl acid maleate and styrene, saidmaleate and styrene beingcopolymerized in a molal ratio between 1:1 and1:2, (2) a minor proportion, based on said copolymer, of polyvinylbutyral and (3) a small proportion of a methyl ether of methylolmelamine, said copolymer, butyral and methyl ether being at least partlyinter-reacted.

HORACE WOOD, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Great Britain June 8, 1937

1. A METHOD OF PRODUCING TRACING CLOTH WHICH COMPRISES IMPREGNATING AWOVEN COTTON FABRIC WHICH IS SUITABLE AS A BASE FOR TRACING CLOTH WITHAN ORGANIC SOLVENT SOLUTION COMPRISING (1) FROM 5 TO 30% BY WEIGHT OF ACOPOLYMER CONSISTING OF A SECONDARY ALKYL HALF ESTER OF AN ETHYLENE A,BDICARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF MALEIC ANDFUMARIC ACIDS, AND A POLYMERIZABLE VINYL COMPOUND HAVING THE STRUCTURALFORMULA: R-CH=CH2, WHERE R IS SELECTED FROM THE GROUP CONSISTING OF APHENYL, HALOGEN SUBSTITUTED PHENYL AND METHYL SUBSTITUTED PHENYLRADICAL, SAID HALF ESTER AND VINYL COMPOUND BEING COPOLYMERIZED IN AMOLAL RATIO BETWEEN 1:1 AND 1:2, (2) A MINOR PROPORTION, BASED ON SAIDCOPOLYMER, OF POLYVINYL BUTYRAL, (3) FROM 0.5 TO 5% BY WEIGHT OF ACOMPOUND SELECTED FROM THE GROUP CONSISTING OF FORMALDEHYDE,PHENOL-FORMALDEHYDE RESINS, UREA-ALDEHYDE RESINS, ALKOXY ALKYL ALKYLMELAMINE RESINS, ALKYLENE POLYAMINES AND ALKYL MELAMINE RESINS, ALKYLENEPOLYAMINES AND POLYGLYCOLS AND (4) AN ORGANIC SOLVENT FOR THE FOREGOINGINGREDIENTS, SAID SOLUTION COMPRISING FROM 6 TO 32% BY WEIGHT OF SOLIDS;DRYING SAID FABRIC AND THEN FRICTION-CALENDERING SAID FABRIC.